GPAT3 encodes a mammalian, microsomal acyl-coa:glycerol 3- phosphate acyltransferase

Abstract

The present invention provides isolated and purified polynucleotides and polypeptides related to mouse and human microsomal acyl-CoA:glycerol 3-phosphate acyltransferase 3 (GPAT3) and their uses in modulating triacylglycerol (TAG) levels in a cell or sample of interest. The invention also provides GPAT3 agonists and antagonists, e.g., GPAT3 polynucleotides and polypeptides, antibodies to GPAT3 (agonistic and antagonistic antibodies), GPAT3 inhibitory polypeptides, and GPAT3 inhibitory polynucleotides. The present invention is also directed to novel methods for diagnosing, prognosing, monitoring, treating, ameliorating and/or preventing conditions related to GPAT3, TAG synthesis (or accumulation), or the synthesis (or accumulation) of TAG precursors (e.g., MAG, LPA, PA, and/or G3P). These GPAT3-associated conditions include, but are not limited to, dyslipidemia (e.g., hyperlipidemia, hypertriglyceridemia, Type III hyperlipidemia), obesity, hypercholesterolemia, hepatic steatosis, cancer, skin disorders associated with altered lipid metabolism (e.g., acne vulgaris, dry skin), adiposity, type 2 diabetes (and complications associated therewith, such as dermopathy, retinopathy, neuropathy, and nephropathy), insulin resistance, hyperinsulinemia, hypertension, cardiovascular disease, atherosclerosis, stroke, thrombosis, lipodystrophy, lipopenia, Reye's syndrome, Cushing's syndrome, metabolic syndrome (e.g., syndrome X), eating disorders (e.g., anorexia, bulimia), skin homeostasis, disorders related to energy storage, nutrient absorption, and lipid metabolism, reduced or absent lactation, and low preterm birth weight (and complications thereof, such as defects in neural development).

1 . A method for treating, ameliorating, or preventing a GPAT3-associated condition in a mammal comprising administering to the mammal a therapeutically effective amount of an agent that modulates the level of expression or activity of GPAT3 in the mammal.  
     
     
         2 . The method as set forth in  claim 1 , wherein the agent is selected from the group consisting of GPAT3 inhibitory polynucleotides or fragments thereof, GPAT3 inhibitory polypeptides or fragments thereof, antagonistic anti-GPAT3 antibodies, antagonistic anti-GPAT3 antibody fragments, and small molecules.  
     
     
         3 . The method as set forth in  claim 1 , wherein the agent is selected from the group consisting of GPAT3 polynucleotides or fragments thereof, polynucleotides that hybridize under high stringency conditions to a complement of the nucleic acid sequence or a fragment of the nucleic acid sequence as set forth in SEQ ID NO:1 or SEQ ID NO:3, GPAT3 polypeptides or fragments thereof, polypeptides encoded by a nucleic acid sequence or a fragment of a nucleic acid sequence as set forth in SEQ ID NO:1 or SEQ ID NO:3, polypeptides encoded by a nucleic acid that hybridizes under high stringency conditions to a complement of the nucleic acid sequence or a fragment of the nucleic acid sequence as set forth in SEQ ID NO:1 or SEQ ID NO:3, agonistic anti-GPAT3 antibodies, agonistic anti-GPAT3 antibody fragments, and small molecules.  
     
     
         4 . A method for decreasing TAG synthesis and/or PA, LPA and/or DAG synthesis and/or accumulation in a cell or cell population, comprising contacting the cell or cell population with a GPAT3 antagonist in an amount sufficient to decrease the level of expression or activity of GPAT3 in the cell or cell population, wherein the GPAT3 antagonist is selected from the group consisting of GPAT3 inhibitory polynucleotides or fragments thereof, GPAT3 inhibitory polypeptides or fragments thereof, antagonistic anti-GPAT3 antibodies, antagonistic anti-GPAT3 antibody fragments, and small molecules.  
     
     
         5 . A method for increasing TAG synthesis and/or PA, LPA and/or DAG synthesis and/or accumulation in a cell or cell population, comprising contacting the cell or cell population with a GPAT3 agonist in an amount sufficient to increase the level of expression or activity of GPAT3 in the cell or cell population, wherein the GPAT3 agonist is selected from the group consisting of GPAT3 polynucleotides or fragments thereof, polynucleotides that hybridize under high stringency conditions to a complement of the nucleic acid sequence or a fragment of the nucleic acid sequence as set forth in SEQ ID NO:1 or SEQ ID NO:3, GPAT3 polypeptides or fragments thereof, polypeptides encoded by a nucleic acid sequence or a fragment of a nucleic acid sequence as set forth in SEQ ID NO:1 or SEQ ID NO:3, polypeptides encoded by a nucleic acid that hybridizes under high stringency conditions to a complement of the nucleic acid sequence or a fragment of the nucleic acid sequence as set forth in SEQ ID NO:1 or SEQ ID NO:3, agonistic anti-GPAT3 antibodies, agonistic anti-GPAT3 antibody fragments, and small molecules.  
     
     
         6 . A method for monitoring the course of a treatment of a GPAT3-associated condition in a patient, comprising: 
 (a) measuring the level of expression or activity of GPAT3 in a cell or sample of interest from the patient;    (b) administering a GPAT3 antagonist to the patient; and    (c) measuring the level of expression or activity of GPAT3 in a cell or sample of interest from the patient following administration of the GPAT3 antagonist,    wherein a lower level of expression or activity of GPAT3 in the cell or sample of interest from the patient following administration of the GPAT3 antagonist, in comparison to the level of expression or activity of GPAT3 in the cell or sample of interest from the patient prior to administration of the GPAT3 antagonist, provides a positive indication of the treatment of the GPAT3-associated condition in the patient.    
     
     
         7 . A method for monitoring the course of a treatment of a GPAT3-associated condition in a patient, comprising: 
 (a) measuring the level of expression or activity of GPAT3 in a cell or sample of interest from the patient;    (b) administering a GPAT3 agonist to the patient; and    (c) measuring the level of expression or activity of GPAT3 in a cell or sample of interest from the patient following administration of the GPAT3 agonist,    wherein a greater level of expression or activity of GPAT3 in the cell or sample of interest from the patient following administration of the GPAT3 agonist, in comparison to the level of expression or activity of GPAT3 in the cell or sample of interest from the patient prior to administration of the GPAT3 agonist, provides a positive indication of the treatment of the GPAT3-associated condition in the patient.    
     
     
         8 . A method for prognosing a GPAT3-associated condition in a patient, comprising: 
 (a) measuring the level of expression or activity of GPAT3 in a cell or sample of interest from the patient at a first time point; and    (b) measuring the level of expression or activity of GPAT3 in a cell or sample of interest from the patient at a second time point,    wherein a different level of expression or activity of GPAT3 in the cell or sample of interest from the patient at the second time point, in comparison to the level of expression or activity of GPAT3 in the cell or sample of interest from the patient at the first time point, indicates a decreased likelihood that the patient will develop a more severe form of the GPAT3-associated condition.    
     
     
         9 . A method for prognosing a GPAT3-associated condition in a patient, comprising: 
 (a) measuring the level of expression or activity of GPAT3 in a cell or sample of interest from the patient; and    (b) comparing the level of expression or activity of GPAT3 in the cell or sample of interest to the level of expression or activity of GPAT3 in a reference cell or sample of interest,    wherein a different level of expression or activity of GPAT3 in the cell or sample of interest from the patient, in comparison to the level of expression or activity of GPAT3 in the reference cell or sample, indicates a decreased likelihood that the patient will develop a more severe form of the GPAT3-associated condition.    
     
     
         10 . A method of screening for a compound capable of modulating GPAT3 activity comprising the steps of: 
 (a) contacting a sample containing GPAT3 with a compound of interest; and    (b) determining whether the level of expression or activity of GPAT3 in the contacted sample is modulated relative to the level of expression or activity of GPAT3 in a sample not contacted with the compound,    wherein a change in the level of expression or activity of GPAT3 in the contacted sample identifies the compound as a compound that is capable of modulating GPAT3 activity.    
     
     
         11 . A pharmaceutical composition comprising a GPAT3 antagonist and a pharmaceutically acceptable carrier.  
     
     
         12 . The pharmaceutical composition of  claim 1   1 , wherein the GPAT3 antagonist is selected from the group consisting of GPAT3 inhibitory polynucleotides or fragments thereof, GPAT3 inhibitory polypeptides or fragments thereof, antagonistic anti-GPAT3 antibodies, antagonistic anti-GPAT3 antibody fragments, and small molecules.  
     
     
         13 . A pharmaceutical composition comprising a GPAT3 agonist and a pharmaceutically acceptable carrier.  
     
     
         14 . The pharmaceutical composition of  claim 13 , wherein the GPAT3 agonist is selected from the group consisting of GPAT3 polynucleotides or fragments thereof, polynucleotides that hybridize under high stringency conditions to a complement of the nucleic acid sequence or a fragment of the nucleic acid sequence as set forth in SEQ ID NO:1 or SEQ ID NO:3, GPAT3 polypeptides or fragments thereof, polypeptides encoded by a nucleic acid sequence or a fragment of a nucleic acid sequence as set forth in SEQ ID NO:1 or SEQ ID NO:3, polypeptides encoded by a nucleic acid that hybridizes under high stringency conditions to a complement of the nucleic acid sequence or a fragment of the nucleic acid sequence as set forth in SEQ ID NO:1 or SEQ ID NO:3, agonistic anti-GPAT3 antibodies, agonistic anti-GPAT3 antibody fragments, and small molecules.  
     
     
         15 . An antibody or antibody fragment that specifically binds a GPAT3 polypeptide or a fragment of a GPAT3 polypeptide.  
     
     
         16 . The antibody or antibody fragment as set forth in  claim 15 , wherein the GPAT3 polypeptide is a mouse GPAT3 polypeptide or a human GPAT3 polypeptide.  
     
     
         17 . The antibody or antibody fragment as set forth in  claim 16 , wherein the GPAT3 polypeptide comprises the amino acid sequence set forth in SEQ ID NO:2 or SEQ ID NO:4.  
     
     
         18 . The antibody or antibody fragment as set forth in any one of claims  15 - 17 , wherein the antibody antagonizes at least one GPAT3 activity.  
     
     
         19 . The antibody or antibody fragment as set forth in any one of claims  15 - 17 , wherein the antibody agonizes at least one GPAT3 activity.